The story concerns the Waterbury family who move to "Three Chimneys", a house near the railway after the father, who works at the Foreign office, is imprisoned as a result of being falsely accused of selling state secrets to the Russians. The three children, Roberta (Bobbie), Peter and Phyllis, find amusement in watching the trains on the nearby railway line and waving to the passengers. They become friendly with Albert Perks, the station porter, and with the Old Gentleman who regularly takes the 9:15 down train. He is eventually able to help prove their father's innocence, ...